Measurement of longitudinal spin transfer toΛhyperons in deep-inelastic lepton scattering

Abstract

Spin transfer in deep-inelastic ⌳ electroproduction has been studied with the HERMES detector using the 27.6 GeV polarized positron beam in the DESY HERA storage ring. For an average fractional energy transfer ͗z͘ϭ0.45, the longitudinal spin transfer from the virtual photon to the ⌳ has been extracted. The spin transfer along the ⌳ momentum direction is found to be 0.11Ϯ0.17(stat)Ϯ0.03(syst); similar values are found for other possible choices for the longitudinal spin direction of the ⌳. This result is the most precise value obtained to date from deep-inelastic scattering with charged lepton beams, and is sensitive to polarized up quark fragmentation to hyperon states. The experimental result is found to be in general agreement with various models of the ⌳ spin content, and is consistent with the assumption of helicity conservation in the fragmentation process.

Effect of sea quarks on single-spin asymmetriesANW±in transversely polarized pp collisions at RHIC

“…Ever since then, the transverse single spin asymmetry (TSSA) has inspired interests both in experimental and theoretical studies. In experimental aspect, the semi-inclusive deep inelastic scattering process (SIDIS) by the HERMES [2][3][4][5] and SMC [6] collaborations and the hadronic reactions in pp collision by the STAR collaboration at RHIC [7,8] have revealed a large transverse single-spin asymmetry with a clear kinematic dependence on the transverse momentum of the hadron as well as on the Feynman variables. Also the related asymmetries are found to be sizable, up to 40%.…”

Transversity in the chiral quark-soliton model and single spin asymmetries

“…In principle one could conclude from data, how well this approximation works. However, the upper x-cut is x < 0.4 in the HERMES experiment [19,20]. 7 Actually, our approach would imply the vanishing of the Sivers effect.…”

“…(x, π) weighted by W (φ) = sin φ (solid line) and sin 2φ (dashed line) for the production of π 0 , π + and π − as function of x. The experimental data are from [19,20]. Rhombus (squares) denote data…”

“…). [19,20] for π + and π 0 production combined. Now let us reverse the logic, and using z-dependence of the HERMES results for the π 0 and π + azimuthal asymmetries try to estimate H ⊥ 1 (z)/D 1 (z).…”

“…Concerning the large value of A sin(φ+φs) 0T (π 0 ) notice that it is approximately of the same order as A sin(φ+φs) 0T (π − ). Meanwhile from the factorization of x and z dependence of polarized and unpolarized SIDIS cross sections and from relation (18) one can write for any spin asymmetry A(π 0 ) = σ(π + ) σ(π + ) + σ(π − ) A(π + ) + σ(π − ) σ(π + ) + σ(π − ) A(π − ) = A(π − ) + a[A(π + ) − A(π − )] , (20) where σ(π) is unpolarized SIDIS cross section. If A(π 0 ) ≈ A(π − ) then a = σ(π + ) σ(π + )+σ(π − ) ≈ 0 that is nonsense!…”